Arcing is a well-known phenomena that results when the current in an electrical circuit is interrupted, wherein an arc is formed across the newly created gap in the circuit. If the arc is not quickly extinguished, for example by containment, cooling, insufficient voltage/current, etc., the intense heat generated by the arc may damage, if not combust, nearby materials and components. Accordingly, special precautions must be taken in the design of switches, relays, fuses and circuit breakers that are intended for use in high-power circuits. It is more difficult, however, to control unintended circuit interruptions that nevertheless may occur due to an inadvertent abusive situation (e.g., tool dropped on a battery pack; battery pack dropped; car crash which causes damage to the battery pack, etc.).
In a typical battery pack, fuses are used to mitigate the effects of an inadvertent short circuit. In some instances, the fuse is placed in series with one, or both, interconnects that couple the battery pack to the load (FIG. 1). If the battery pack includes a plurality of cells as illustrated in FIG. 2, the battery pack may still rely on a single fuse as shown in FIG. 1, or each cell may be connected via its own fuse or fusible interconnect as shown in FIG. 2.
Regardless of the approach used to provide circuit protection, it is desirable that the fusing element(s) of the circuit fuse quickly enough to avoid damage or excessive heating of adjacent cells/components. This is especially desirable in battery packs utilizing a large number of cells packed closely together as excessive heating may quickly initiate thermal runaway in one or more cells. During a thermal runaway event, a large amount of thermal energy is rapidly released, heating the entire cell up to a temperature of 900° C. or more. Due to the increased temperature of the cell undergoing thermal runaway, the temperature of adjacent cells within the battery pack will also increase, an effect that is exacerbated by the close packing of cells in a large battery pack. If the temperature of these adjacent cells is allowed to increase unimpeded, they may also enter into a state of thermal runaway, leading to a cascading effect that may propagate throughout the entire battery pack. As a result, not only is power from the battery pack interrupted, but the system employing the battery pack is more likely to incur extensive collateral damage due to the scale of thermal runaway and the associated release of thermal energy.
In a battery pack in which the cells are connected in parallel, as illustrated in FIG. 2, when a short circuit occurs it is distributed among all of the cells. As a result, typically the fuses/fusible interconnects will blow one after another until all of the fuses/fusible links have blown. The order in which these fuses/fusible links blow will depend upon minor variations between each fuse/fusible interconnect, such as differences in thermal mass, electrical impedance, etc. The last fuse/fusible interconnect within the group of cells is the fuse/fusible interconnect that is most likely to arc. In a conventional battery pack, as the order in which the fuses/fusible interconnects blow is not controlled, each fuse/fusible interconnect must be designed to minimize the risk of arcing, or other means must be employed to mitigate the potential effects of arcing. This approach, however, leads to increased cost, complexity and weight, all of which may be quite significant in large battery packs such as those employed in hybrid and all-electric vehicles. Accordingly, what is needed is a means of minimizing the risks associated with arcing within a battery pack, while not significantly impacting battery pack manufacturing cost, complexity and weight. The present system provides such a means.